Project Summary Falls from ladders cause severe injuries and fatalities among workers. Despite well-established epidemiology that identifies slips and falls from ladders as an important problem, little is known regarding how ladder design or an individual's body affects slip and fall risk. Furthermore, no tests exist to assess the friction performance of ladder rungs. This knowledge gap is a major barrier in designing safer ladders and verifying their efficacy. The objective of this NIOSH R01 research study is to develop new methods for assessing friction performance of ladder rungs, friction requirements of ladder climbing, and their relationship with the occurrence of slipping during ladder climbing. The long-term goal of our research is to develop a set of ladder safety guidelines (ladder design guidelines and safe climbing guidelines) that can lead to a substantive reduction in the number of severe injuries and fatalities caused by ladder slip-and-fall events. This research is a continuation of an existing line of research (originally funded by a NIOSH R21 grant) where we have developed novel methods of measuring human subject responses to perturbations during ladder climbing. The preliminary research by the team has led to five published peer-review papers (and a sixth in review) as well as 15 conference abstracts/proceedings. The study consists of four aims. Aim 1: Quantify the impact of ladder design on required coefficient of friction (RCOF). Based on preliminary data, we hypothesize that friction requirements will be influenced by the angle of the ladder (H1.1) and the rung design (shape: H1.2; size: H1.3). Aim 2: Quantify the impact of the individual factors, height, obesity, and sex, on RCOF. We hypothesize that height (H2.1) will be negatively correlated with friction requirements. Furthermore, we hypothesize that differences will exist across obesity groups (H2.2) and sexes (H2.3). Aim 3: Quantify the impact of ladder design on traction performance, measured by the available coefficient of friction (ACOF). We hypothesize that rungs designated as ?non-slip? will perform better than those without this designation (H3.1); and that size (H3.2), orientation (H3.3) and shape (H3.4) will influence friction performance. Aim 4: Identify the ACOF measurement methods that best predict slipping. We hypothesize that slipping can be predicted with available friction and friction requirements (H4.1) and that different testing methods will vary in their ability to predict slipping (H4.2). This research project is expected to lead to specific ladder design interventions for safer ladders such as recommendations for ladder angle, rung size, and rung shape. Furthermore, this project is expected to lead to new validated testing methods that can be utilized in industry to discriminate between high and low traction rung designs to enable future innovations in ladder safety design. This research addresses several of NIOSH's Program Grid Intermediate Goals that mention falls from different levels or falls from ladders: 6.2(A) (Construction), 6.13 (B) (Services), 6.16 (B) (Wholesale/Retail), 6.18 (A) (Mining).